1. Field of the Invention
The present invention relates to a three-dimensional location measurement sensor, which measures the location of a target object and the distance between the three-dimensional location measurement sensor and the target object, and a method of measuring the location of a target object and the distance between the three-dimensional location measurement sensor and the target object.
2. Description of the Related Art
Various location measurement methods and devices have been developed. Many conventional location measurement methods and devices use trigonometric methods to determine the location of an object by measuring the direction of the object with respect to a reference point and a distance between the object and the reference point. Recently, the importance of such location measurement methods and devices has gradually increased due to the development of home robots or high-speed mobile devices.
The location of an object with respect to the location of measurement sensor (hereinafter referred to as a reference point) may be expressed by using three location variables, which will be described more fully with reference to FIG. 1. Referring to FIG. 1, suppose that O is the reference point, A is a target object, Φ is an azimuth angle of the target object A when a location of the object A is projected on the xy plane, Ψ is an inclination angle to represent the slope of a straight line between O and A. Lastly, r is a distance between O and A. Therefore, the location of the target object A may be determined by determining values of Φ, Ψ, and r. The three location variables Φ, Ψ, and r may vary together or independently of one another. Precisely determining the three location variables Φ, Ψ, and r to determine the location of the target object is crucial.
The conventional location measurement devices are classified into two groups depending on how they determine the location of a target object. A first group of conventional location measurement devices determine the location of the target object by appropriately panning and/or tilting a distance measurement device or a camera. A second group of conventional location measurement devices determine the location of the target object by using beams that are reflected from a mirror.
A conventional location measurement device in the first group should drive a distance measurement device or a camera. Thus, the first group location measurement device requires a driving unit to generate a considerable amount of driving force. An additional characteristic of the first group location measurement device is that rotating the device at a high speed while determining the location of a target object is difficult.
An example of the conventional location measurement device in the first group is disclosed in U.S. Pat. No. D474489S (Cannon 2002). In U.S. Pat. No. D474489S, a driver is attached to one of a distance measurement device, an inclination angle control axis, or an azimuth angle control axis of a camera so that driving the distance measurement device or the camera in order to measure an azimuth angle may be performed independently of driving the distance measurement device or the camera in order to measure an inclination angle of the target object. However, the conventional location measurement device disclosed in U.S. Pat. No. D474489 cannot rotate indefinitely.
Another example of the conventional location measurement device is disclosed in U.S. Pat. No. 6,479,813. The '813 patent teaches controlling an azimuth angle independently of an inclination angle. The '813 patent also teaches that rotating indefinitely is possible due to a slip ring. However, when transmitting analog signals with the use of the slip ring, the analog signals may be distorted.
U.S. Pat. No. 4,886,330 discloses an infrared imaging system in which an azimuth angle and an inclination angle can be controlled using a single motor. The patented infrared imaging system, however, cannot set the azimuth angle and the inclination angle on the basis of an arbitrary location.
A conventional location measurement device in the second group measures the azimuth and inclination angles of a target object with respect to a reference location and the distance from the reference location to the target object by driving a mirror. With respect to these devices, even when the target object moves, the conventional location measurement device may determine the location of the target object because only a small portion of the conventional location measurement device is driven when determining the location of the target object.
An example of the conventional location measurement device is disclosed in U.S. Pat. No. 4,945,459 in which two motors are provided to control the azimuth and inclination angles of a corresponding conventional location measurement device independently of each other. However, miniaturizing the conventional location measurement device disclosed in the '459 patent is relatively difficult because the conventional location measurement device needs to use a unique chain.
In short, the above-described conventional location measurement sensors (or devices) have the following disadvantages.
First, due to the limitations of a platform on which the conventional location measurement sensors are mounted, the conventional location measurement sensors cannot rotate within a range of 0–360 degrees. Therefore, a clear limit in determining the location of a target object that rotates more than 360 degrees exists.
Second, in some of the conventional location measurement sensors, an azimuth angle is dependent upon an inclination angle, and vice versa, in which case, precisely determining the distance from a reference location to a target object located in an arbitrary direction is substantially impossible.
Third, some conventional location measurement sensors use an omnidirectional mirror that provides a 360 degree field of view to a camera, in which case, the area of a region the camera needs to deal with increases resulting in a decrease in the resolution of an image of the region taken by the camera.